Not really a backfire, just a pop - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Army_Dude · 02-17-2006, 12:06 AM

Ever since I've had my truck (about 3 months now) It has done this. Since I got it I have changed the dist cap, plugs, wires, and checked the timing. The timing was way advanced so I brought it down, then took it up a little due to a test drive. I've done other things but nothing I think would affect this. As I said it has always done it.

Only at idle it seems. It will pop out of the tailpipe. Sounds kinds like a mini-backfire. It isn't constant probably about every other puff from the exhaust. I'm not sure but I think it is coming from the right side pipe (Pass side). Any ideas?

crackajacka · 02-17-2006, 01:12 AM

i really dont know what would cause it but i know what u mean. when i had my old 305 in my truck i could make it sound like popcorn popping by reving it constantly inbetween 2200-2600rpms. I also had glass packs on it running straight out the back with long chrome tips also. that might be your problem if u have them. i changed my exhaust to dump at the axels when i put in a crate 350 and the problem quit. Thats how my situation was hope it helps u figure out what's causing the pops

72 CustomCamper · 02-17-2006, 01:34 AM

Sounds like it's running a little rich (too much fuel). It could need the carb adjusted or it could be the choke is closed too much...

Chuck

Army_Dude · 02-17-2006, 03:24 AM

how do I tune the carb. I am aware of the air/fuel screw. Know jack about the choke.

We could be onto something here, I am yet to fool with the carb.

tgh117 · 02-17-2006, 01:17 PM

might want to check the pass side plugs. My truck the motor is getting old and tired and has a tendancy to junk up the plugs in the rear of the pass side. When the truck sits and idles it will pop until the spark plug heats up enough to spark and function properly. Does it pretty much at any rpm for the first 5-7 min of running.

**swervin ervin** · 02-17-2006, 06:02 PM

Could also be a sticking or burnt valve. Weak valve spring. Several things it could be but it's just a matter of narrowing it down to the right thing. Let's hope it's a spark plug or carb out of tune.

chevyjr73 · 02-17-2006, 06:18 PM

my 86 had an annoying pop i chased down for awhile. mine didn't do it at idle though but while decelerating. turned out i had a bad air pump diverter valve.

piecesparts · 02-18-2006, 06:48 PM

Do you still have the catalytic convertor? If you have a tendency to run a little rich in a fuel mixture, there can be moments where there is a burn in the exhaust and converter area. This is not a common thing, but it could happen.

I would also look at the possibility of corbon build-up in the cylinders and on the exhaust valves. If these get a hot spot, then there can be an after ignition scenario going on. As the unbrnt gases are leaving the cylinder, then the hot carbon would ignite the remaining fuel.

Third look for a burnt valve problem, as a last resort.

02-17-2006, 12:06 AM	#1
Army_Dude Registered User Join Date: Dec 2005 Location: Fayetteville, NC Posts: 187	Not really a backfire, just a pop Ever since I've had my truck (about 3 months now) It has done this. Since I got it I have changed the dist cap, plugs, wires, and checked the timing. The timing was way advanced so I brought it down, then took it up a little due to a test drive. I've done other things but nothing I think would affect this. As I said it has always done it. Only at idle it seems. It will pop out of the tailpipe. Sounds kinds like a mini-backfire. It isn't constant probably about every other puff from the exhaust. I'm not sure but I think it is coming from the right side pipe (Pass side). Any ideas?

02-17-2006, 01:12 AM	#2
crackajacka Stylin Join Date: Sep 2001 Location: Tuttle, OK Posts: 620	Re: Not really a backfire, just a pop i really dont know what would cause it but i know what u mean. when i had my old 305 in my truck i could make it sound like popcorn popping by reving it constantly inbetween 2200-2600rpms. I also had glass packs on it running straight out the back with long chrome tips also. that might be your problem if u have them. i changed my exhaust to dump at the axels when i put in a crate 350 and the problem quit. Thats how my situation was hope it helps u figure out what's causing the pops __________________ Ive been traveling for some time, with my fishin pole and my bottle of shyne. Most Girls like finished products and just dont understand what a good addiction does for you http://www.paulwall.us/

02-17-2006, 01:34 AM	#3
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,369	Re: Not really a backfire, just a pop Sounds like it's running a little rich (too much fuel). It could need the carb adjusted or it could be the choke is closed too much... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

02-17-2006, 03:24 AM	#4
Army_Dude Registered User Join Date: Dec 2005 Location: Fayetteville, NC Posts: 187	Re: Not really a backfire, just a pop how do I tune the carb. I am aware of the air/fuel screw. Know jack about the choke. We could be onto something here, I am yet to fool with the carb.

02-17-2006, 01:17 PM	#5
tgh117 Crazy Join Date: Apr 2005 Location: Emmaus, Pa Posts: 203	Re: Not really a backfire, just a pop might want to check the pass side plugs. My truck the motor is getting old and tired and has a tendancy to junk up the plugs in the rear of the pass side. When the truck sits and idles it will pop until the spark plug heats up enough to spark and function properly. Does it pretty much at any rpm for the first 5-7 min of running. __________________ 77 SB Stepside in a bunch of pieces scattered around the garage.

02-17-2006, 06:02 PM	#6
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Re: Not really a backfire, just a pop Could also be a sticking or burnt valve. Weak valve spring. Several things it could be but it's just a matter of narrowing it down to the right thing. Let's hope it's a spark plug or carb out of tune. __________________ Mike 1985 Chevy C-10

02-17-2006, 06:18 PM	#7
chevyjr73 Registered User Join Date: Mar 2004 Location: chesapeake,virginia Posts: 117	Re: Not really a backfire, just a pop my 86 had an annoying pop i chased down for awhile. mine didn't do it at idle though but while decelerating. turned out i had a bad air pump diverter valve.

02-18-2006, 06:48 PM	#8
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: Not really a backfire, just a pop Do you still have the catalytic convertor? If you have a tendency to run a little rich in a fuel mixture, there can be moments where there is a burn in the exhaust and converter area. This is not a common thing, but it could happen. I would also look at the possibility of corbon build-up in the cylinders and on the exhaust valves. If these get a hot spot, then there can be an after ignition scenario going on. As the unbrnt gases are leaving the cylinder, then the hot carbon would ignite the remaining fuel. Third look for a burnt valve problem, as a last resort.



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